Recent developments in the lighting field have allowed for the use of a centralized lighting system to be applied to a variety of product areas where it is desirable to utilize a single light source and a plurality of optical fibers to distribute the high brightness light output from the light source to at least one location remote from the light source. As an example, a centralized lighting system has been proposed for automotive uses where a light source could be disposed under the hood of the vehicle and the light for forward lighting, or interior panel lights could be delivered over optical fibers. An example of such a centralized lighting system can be found in Davenport et al U.S. Pat. No. 4,958,263 on Sep. 18, 1990 and assigned to the same assignee as the present invention. In this patent, a light source is provided having a central ellipsoidally shaped arc tube and a number of extending tube shaped extensions formed thereon. Each of the extending tube portions is coupled over optical fibers to various locations around a vehicle for providing lighting needed for forward illumination, tail lighting and overhead lighting for instance. Centralized lighting systems have been proposed for other areas as well such as for instance, for displaying merchandise in a retailing environment where it is desirable to illuminate certain merchandise in a favorable manner. By the use of a centralized lighting system for such an application, an optical fiber can be used to provide light output which is uniform in color and intensity and, furthermore, will not expose the merchandise to the heat or other radiation of a conventional display lighting arrangement.
Still another application of a centralized lighting system would be in a projection lighting system such as a message display at a sports arena or other setting where information or images are displayed to large numbers of people from a single display board. One of the problems associated with displaying information or images on a large screen display board from a centralized light source is in achieving a sufficient number of distinct output levels to convey the intended information or display the appropriate image. For a centralized light source that does not include a light switching arrangement, logic would dictate that there are two possible light outputs for each optical fiber, one being defined as a light "on" condition and the other as the light source being "off". Accordingly, in order for a centralized lighting system to be advantageous to a display board application, it will be necessary to include a light switching arrangement that could provide various levels of light output. Such a switching arrangement must simultaneously provide the characteristics of: high contrast ratios (e.g. greater than 100:1), low insertion loss (e.g. greater than 90% Transmission), speeds which are greater than video rates, and a greyscale control of at least 8 levels. New polymer piezoelectric materials have allowed for the development of light switching techniques that have satisfied the first three of these characteristics; that is, high contrast ratios, low insertion losses and high speeds. For example, U.S. Pat. No. 5,052,777 issued to Ninnis et al on Oct. 1, 1991 describes a graphic display arrangement using bimorph gate devices as light switches. Though effective for achieving high contrast ratios, low insertion losses and high speed, as to the need to provide greyscale control of at least eight levels, present techniques have been inadequate. For instance, using a pulse width modulation technique for switching the piezoelectric or bimorph gate device would yield a greyscale control having 3 different levels corresponding to "on", "off", and "half-on/half-off". This three level arrangement comes about by way of changing the image rate of operation for the bimorph gate device. One way to increase the number of greyscale levels using piezoelectric switches or shutters, would be to provide an array of such switches for each intended pixel of light output. Unfortunately, such an arrangement would be severely disadvantageous because of the cost factor for the arrays of switches and furthermore, because of the space requirements for such devices. Therefore, in designing a centralized lighting system that provided for at least eight levels of greyscale control, it would be advantageous to provide an arrangement that did not require a large number of piezoelectric shutters, and yet, still achieved all of the necessary operating characteristics such as high contrast ratio, low insertion losses, and speed.